As indicated above, the present invention is particularly directed toward pressure filter systems and more preferably toward such a pressure filter system employed for supplying filtered fluid to a process or system characterized by varying demands for filtered fluid.
Process systems of the type referred to above include, for example, metalworking processes such as two-piece D&I can manufacturing and rolling mills for aluminum or other metals where a coolant/lubricant is used in the metalworking process and then is reconditioned in a filter system to remove undesirable contaminants and to permit recycling of the fluid for continued use in the process.
Other process systems of the type referred to above include chemical processes such as ink and paint manufacturing, electroplating and metal surface treating processes, etc., automotive applications, waste water treatment and food and beverage processing. Numerous other examples of processing systems contemplated by the present invention will also be obvious from the typical processes described above.
Pressure filters employed in connection with such process systems typically utilize a porous membrane or filter media through which the fluid is forced under pressure in order to remove particulate materials or contaminants, and thus to recondition the fluid for reuse in processes such as those described above.
The porous filter media is commonly supplied in rolls so that it can readily be replaced within the filter assembly or chamber. A portion of the filter media which has received a substantial accumulation or build-up of contaminants tending to produce a processing limiting pressure drop across the filter media is simultaneously removed from the filter assembly for disposal.
A basic filtering method of the type described above is commonly referred to as pad filtration and may employ a porous filter media by itself for removing contaminants from fluid passing therethrough. Such applications typically employ a filter media of a type adapted for either surface, or surface and depth filtration. Pad filtration of this type is satisfactory particularly if it results in the efficiency of filtration required by the application, and in relatively long filter cycles without an excessive requirement for replacement of the spent filter media.
For application where unique problems must be dealt with or extremely efficiency filtration must be achieved, filter aids are commonly used. Filter aid materials of the type described below are precoated onto the filter media for increased efficiency, and/or unique capability. Such filter aid material may be deposited onto a porous support media for example to a thickness of about 1/16 inch for this purpose.
The capacity of a filter media, particularly in terms of its operating duration prior to the need for replacing the filter media, may be further increased by both precoating and bodyfeeding filter aid materials onto the surface of the support media. In such applications, filter aid materials are initially deposited or precoated onto the filter media as described above with additional filter aid material being included or bodyfed with the fluid to be filtered. In this manner, the filter aid materials supplied by bodyfeeding operations tend to continuously deposit upon the filter media during each filter operating cycle, and thereby continuously renew the surface of the filter media as described in greater detail below in order to again improve capacity by still further extending the operating cycle life for the filter media.
Thus, pressure filter systems of the type referred to above frequently employ various filter aids in order to improve both efficiency and capacity of the filter. Typical filter aid materials include, for example, diatomaceous earth, cellulosic materials, burned rice hulls, Fuller's Earth, Bentonite, Attapulgite, Perlite, etc. Additional filter aid materials are also described and listed below. Generally, these filter aids may be precoated onto the filter media, or precoated and continuously bodyfed to the filter media during filtration, for example in a precoat and bodyfeed operation as described in greater detail below.
Filter aids are generally applied to the filter initially by precoating the filter elements to establish the initial filter septurn. In an effort to prevent the precoated media from quickly blinding across its surface with contaminants, additional filter aid is continuously or intermittently applied to the filter septum in order to continuously renew the filter surface. This process is referred to as bodyfeeding. By bodyfeeding filter aid to the filter septum along with the contaminants to be removed, filtration is accomplished by retention of contaminants throughout the accumulated cake and filter aid materials. In so doing, the pressure drop across the filter develops in a relatively linear relationship with time (assuming flow rates and contaminant loading are constant). Without bodyfeeding, filtration would occur at the surface of the pre-established filter septum and surface blinding would occur causing the pressure drop across the filter to develop in an exponential relationship with time, resulting in significantly shorter filter cycles and reduced filter capacity.
Filter aids of the type referred to above may be selected for simple physical entrapment of particles and typically include generally non-polar materials such as diatomaceous earth and the like. Other systems may employ filter aids which are polar materials such as Fuller's Earth, Bentonite and Attapulgite, etc. These materials are generally referred to as "charged clays". Such polar filter aid materials are particularly desirable for removing extremely small charged particles or "color bodies" from process fluid.
Prior art bodyfeed systems of the type discussed above have been disclosed for example in Pato, U.S. Pat. No. 4,514,306 issued Apr. 30, 1985 under assignment to Monarch Wine Co., Inc., Brooklyn, N.Y.; Strub, U.S. Pat. No. 4,118,778 issued Oct. 3, 1978 under assignment to Filtrox Maschinenbau A. G., St. Gallen, Switzerland; Lane, et al., U.S. Pat No. 2,971,648 issued Feb. 14, 1961 under mesne assignment to Union Tank Car Company, Chicago, Ill.; and in UK Patent Application GB 2 264 882 A, published Sep. 15, 1993 by the Applicant Achenbach Buschhutten GmbH.